Current sense transformers are used to measure current passing through a conductor. Typical applications for current sense transformers are overload sensing, load variation sensing, and electric power metering. The construction of a current sense transformer depends on the desired transformer efficiency, which in turn is dictated by the requirements of the application that uses the current sense transformer.
Current sense transformers that are required to be optimized to work at a very high efficiency typically employ a toroidal winding wherein the secondary winding is wound around a transformer core. These toroidal winding type current sense transformers are expensive to fabricate and therefore not practical for use in applications where transformer efficiency is not critical. Bobbin-wound current sense transformers are less expensive to fabricate than wound core devices, and transformer windings obtained from a simple bobbin machine can be used for these bobbin-wound current sense transformers.
A typical bobbin-wound current sense transformer has a laminated or ferrite core, a primary winding that has a single turn (or small number of turns) and a secondary winding with a large number of turns. The primary and secondary windings are mounted on the core and there are separate primary and secondary terminals connected to the primary and secondary windings respectively. Insulating members separate the primary winding, secondary winding and the core from one another.
During operation a typical current sense transformer has its primary winding connected in series with an alternating current source to be monitored. This current is coupled magnetically by the magnetic core shared by the primary and secondary windings. The current is reduced by the ratio of secondary to primary turns. A resistor is connected across the secondary winding so that the reduced current will flow through the winding and develop a voltage across the resistor. The voltage is dependent upon the value of the resistor connected across the secondary, and the amount of current flowing through the secondary.
The current trend in the electronics industry is to fabricate circuit boards smaller and smaller. As a result, there exists a need for an apparatus and methodology for a reduced size high-frequency surface-mount current sense transformer. There also exists a need for an apparatus and methodology for a current sense transformer with a greater voltage withstand capability.